The present invention relates to a graphics display method and apparatus and particularly to a method and apparatus for providing a wide range of color reproduction in minimum operating time.
Graphics display terminals and the like are not limited to the presentation of multicolor cathode-ray-tube images, but can also produce multicolor hard copy utilizing apparatus such as an ink jet copier. The ink jet copier or printer has a limited number of ink jets which can be employed separately for depositing a single bit or pixel of information on paper, or which can be used together to produce a limited number combination of colors. In a particular example, four colors of ink are used: yellow, cyan, and magenta (subtractive primaries) and black. Red, green, and blue (additive primaries) are formed by superimposing two ink colors on the same dot or pixel. Thus, cyan over yellow results in green, magenta over yellow results in red, and magenta over cyan produces blue. In this manner, the four colors of ink can produce a total of seven solid colors, with the white of the paper supplying an eighth.
However, a much wider range or colors would be desired, for example to match the range of colors which a cathode-ray-tube may be able to provide. Unfortunately, ink jets and the like are for the most part only capable of being turned on or turned off, while the mixing or various colors to form a multitude of shades would require relative intensities of the primary colors.
Another method of producing the effect of relative color intensity utilizes "dither" patterns, including dots of one color interspersed with dots of another in a correct ratio to form the desired shade. For example, to achieve a mixture of two primaries such as red and yellow, dots of red may be interlaced with dots of yellow, wherein the interlaced arrangement comprises the dither pattern. If there are appreciable numbers of dots or pixels in an area being colored, and if the resulting hard copy is viewed at any distance, the eye combines the colors of the dither pattern to achieve the effect of the desired shade.
The management of the color image including the "rasterizing" of data to supply the individual dots or pixels is usually under the control of a microprocessor. According to the conventional approach, the processor would direct the production of each pixel at each particular location on a piece of paper, and the processor would look up the color information in a table in order to determine what color each pixel should be in order to write the overall dither pattern. This approach slows operation relative to the speed of operation of an ink jet copier apparatus. It would be more desirable for the processor to simply specify a color in advance for a particular area or object, and then merely address the area or object without necessitating the organization of the required dither pattern as well.